His non-fiction books are easy to read and full of lots of wonderful turns-of-phrase. A lot of what he wrote back in the day sounds like it could be written today. There is a fair amount of his books that was very of-the-moment, making references to people from the time that I suppose were well known then that you need to read around.
I've only read two of his fiction books (Napoleon of Notting Hill and The Man who was Thursday), both of which are really funny.